Preheat your oven to 375°F (190°C).

Heat olive oil in a 10-12 inch oven-safe skillet over medium-high heat. Add chicken pieces in a single layer without crowding. Cook undisturbed for 3-4 minutes until golden brown on bottom, then flip and cook 2-3 minutes more until just cooked through. Remove chicken from skillet and set aside.

In the same skillet, add the onion, carrots, and celery. Sauté until vegetables begin to soften, about 5 minutes. Add garlic and cook for another minute until fragrant.

Add butter to the skillet and let it melt completely. Whisk in the flour to form a paste and cook for 1 minute, stirring constantly.

Gradually whisk in the chicken broth and milk until smooth. Add thyme, rosemary, salt, and pepper.

Bring the mixture to a simmer and cook, stirring occasionally, until the sauce thickens enough to coat the back of a spoon, about 5-7 minutes.

Stir in the frozen peas and cooked chicken.

In a small bowl, mix the Greek yogurt and Parmesan cheese. Dollop 6-8 spoonfuls randomly over the surface.

Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the topping is golden and the filling is bubbly.

Let rest for 5 minutes before serving. Garnish with fresh parsley.